1. Field of the Invention
The present invention relates to a resolver abnormality detection apparatus for detecting an abnormality such as a wire breakage or a sky fault (a short circuit to power supply) in a resolver.
2. Description of Related Art
Japanese Patent Application Laid-open No. 2000-166205 describes an interphase short-circuit detection apparatus for a resolver, the apparatus including a DC power supply connected to the cosine phase of the secondary winding of the resolver, a comparator for comparing a DC voltage relative to ground of the sine phase of the secondary winding of the resolver with a threshold value, and a comparator for comparing a DC voltage relative to ground of the cosine phase of the secondary winding of the resolver with a threshold value. This interphase short-circuit detection apparatus can detect an interphase short circuit in the secondary winding, and a short circuit between the primary winding and the secondary winding based on the outputs of the two comparators.
This interphase short-circuit detection apparatus can detect also a sky fault and a ground fault (a short circuit to ground) in the secondary winding. However, in this interphase short-circuit detection apparatus, there is a limit to the rotational angle θ of the rotor of a resolver in detecting a wire breakage in the secondary winding. For example, in a case where a wire breakage is determined to be present in the resolver when the equation of sin (θ)^2+cos (θ)^2=1 does not hold, if there occurs a wire breakage in the sine phase when the rotational angle θ of the rotor is 0 degrees, it cannot be detected, because this equation still holds. Accordingly, this interphase short-circuit detection apparatus has a problem in that when a wire breakage occurs while the rotor is stationary at a specific angle position, the wire breakage may not be detected.